package com.ken.callblock2.tools;

import java.security.SecureRandom;

import javax.crypto.Cipher;
import javax.crypto.KeyGenerator;
import javax.crypto.SecretKey;
import javax.crypto.spec.SecretKeySpec;

/**
 * Usage:
 * <pre>
 * String crypto = SimpleCrypto.encrypt(masterpassword, cleartext)
 * ...
 * String cleartext = SimpleCrypto.decrypt(masterpassword, crypto)
 * </pre>
 * @author ferenc.hechler
 */
public class SimpleCrypto {

    public static String encrypt(String seed, String cleartext) throws Exception {
            byte[] rawKey = getRawKey(seed.getBytes());
            byte[] result = encrypt(rawKey, cleartext.getBytes());
            return toHex(result);
    }
    
    public static String decrypt(String seed, String encrypted) throws Exception {
            byte[] rawKey = getRawKey(seed.getBytes());
            byte[] enc = toByte(encrypted);
            byte[] result = decrypt(rawKey, enc);
            return new String(result);
    }

    private static byte[] getRawKey(byte[] seed) throws Exception {
            KeyGenerator kgen = KeyGenerator.getInstance("AES");
            SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
            sr.setSeed(seed);
        kgen.init(128, sr); // 192 and 256 bits may not be available
        SecretKey skey = kgen.generateKey();
        byte[] raw = skey.getEncoded();
        return raw;
    }

    
    private static byte[] encrypt(byte[] raw, byte[] clear) throws Exception {
        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
            Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, skeySpec);
        byte[] encrypted = cipher.doFinal(clear);
            return encrypted;
    }

    private static byte[] decrypt(byte[] raw, byte[] encrypted) throws Exception {
        SecretKeySpec skeySpec = new SecretKeySpec(raw, "AES");
            Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, skeySpec);
        byte[] decrypted = cipher.doFinal(encrypted);
            return decrypted;
    }

    public static String toHex(String txt) {
            return toHex(txt.getBytes());
    }
    public static String fromHex(String hex) {
            return new String(toByte(hex));
    }
    
    public static byte[] toByte(String hexString) {
            int len = hexString.length()/2;
            byte[] result = new byte[len];
            for (int i = 0; i < len; i++)
                    result[i] = Integer.valueOf(hexString.substring(2*i, 2*i+2), 16).byteValue();
            return result;
    }

    public static String toHex(byte[] buf) {
            if (buf == null)
                    return "";
            StringBuffer result = new StringBuffer(2*buf.length);
            for (int i = 0; i < buf.length; i++) {
                    appendHex(result, buf[i]);
            }
            return result.toString();
    }
    private final static String HEX = "0123456789ABCDEF";
    private static void appendHex(StringBuffer sb, byte b) {
            sb.append(HEX.charAt((b>>4)&0x0f)).append(HEX.charAt(b&0x0f));
    }

}
